Armrests are often inadequate or insufficient in mass transit cabins, such as those found in the coach or economy-classes of most commercial airline aircraft today, especially for passengers seated in an adjacent fashion. Typically in these scenarios, an identically-sized armrest, which is utilized to support passengers seated at the ends of a row of seats (i.e., without the possibility of a passenger being seated next to them on at least one side), is also utilized in between seats where two passengers may be seated immediately next to each other. These passengers will often find it awkward or impossible to share the surface area of the armrest provided and visible signs of passenger discomfort can be easily perceived. Also, these armrests may be require passengers to slouch or lean in order to reach them because of the armrest's inadequate relative height to the passenger's seat.
It is noteworthy that this problem does not typically exist in premium cabins where passengers pay more for additional space. Armrests which separate passengers are typically much larger in all dimensions in these cabins and usually eliminate the need to share a single armrest between passengers. Subsequently, it is assumed that the primary reasons that current technology is insufficient to address the problem have to do with a commercial airline's business goals. Those goals include maximizing the number of passengers, or passenger-seating, within the space of the economy cabins while minimizing the acquisition and maintenance costs of the seating, which is typically installed in the aircraft by a third party. In addition, this problem may also provide airline customers with additional incentives to purchase more comfortable, hence more expensive, seats.
As previously mentioned, the general problem of insufficient armrest space is not unique to aircraft cabins; it may also be found on a variety of commercial vehicles which have been designed for maximum passenger occupancy at the expense of some passenger comfort. Public theaters and viewing venues also commonly present similar problems. Other issues may exist with commercial armrests in general, such as the level of the armrest being lower than would be ergonomically comfortable for a passenger to use, or the armrest surface may be insufficiently soft or padded for a passenger's comfort. These additional issues may be related or unrelated to the primary problem of insufficient space.